Airbags for passenger vehicles commonly use an “inflator” to inflate the airbag in case of an emergency. A typical inflator includes an ignitor and a propellant that inflates an airbag in the event of a vehicle crash. One of the world's largest airbag suppliers—Takata®—has produced a large number of defective airbag inflators. As of November 2016, over 100 million Takata® inflators have been recalled worldwide. The scale of this recall has introduced safety, logistical, and environmental challenges involved with transporting and disposing of explosive and unstable airbag inflators.
The defective inflators use ammonium nitrate (“AN”) propellant. While designed to deploy upon receiving an electrical current at the inflator's initiator pins, the defective inflators can also deploy with exposure to an external heat source such as fire. According to news sources, the current, unregulated process of transporting recalled Takata® airbags has already caused at least 16 deaths. As a result, a comprehensive protocol for ensuring safe transport and disposal of recalled inflators is needed.
To gain approval for shipping on U.S. roads, all production automotive airbag inflators and energetic assemblies, such as seat belt pre-tensioners, are subjected to a Department of Transportation (“DOT”) “bonfire” test. Europe's DOT equivalent, BAM, requires a similar “gas burner” test. Both the DOT and BAM tests involve exposing airbag inflators to an open-flame heat source sufficient to cause auto ignition of the inflator's main generant bed. To pass the test and be approved for shipping, an inflator must function without fragmenting due to the external heat source. Bonfire testing is the most rigorous structural test of an AN-based inflator design because ammonium nitrate propellant can melt before it burns, resulting in conditions inside the inflator that amplify challenges of ensuring the design does not fail structurally during the open flame deployment scenario.
The U.S. government, and other governments around the world, will likely classify AN-based airbag inflators as explosives or change the existing classification for recalled inflators. That new classification (or reclassification) would prevent traditional shipping methods from being used to transport these inflators. AN-based airbag inflators that are known to fragment due to over pressurization of the inflator's pressure vessel housing during normal deployment conditions at ambient outside temperature are generally expected to fail at a higher rate (or are more likely to fail) when exposed to an external heat source such as DOT Bonfire testing. An inflator sample population that exhibits any structural failures when deployed at ambient temperature is likely to exhibit a significantly higher rate of structural failure when an external heat source causes the inflator to deploy. This is because operating pressure of the inflator's internal combustion chamber tends to increase with temperature, while the steel pressure vessel strength decreases with temperature. This problem can become significantly worse if propellant melts.
Common auto-ignition materials ignite at temperatures above 130° C., which is significantly higher than any upper temperature limit the inflator design was intended to operate at during normal deployment conditions. Hence, an inflator suspected of structural failure when functioning at ambient temperature has an increasing likelihood of structural failure as temperature increases. Defective AN-based Takata® inflators can fragment even at ambient outside temperatures. Thus, they are expected to fragment more frequently if exposed to an external fire such as the DOT Bonfire test. These defective inflators are therefore not fit to be shipped using traditional methods used for non-defective inflators.
Currently, these recalled inflators are being shipped in steel drums with lids secured with tape, or in cardboard boxes, depending on the relevant state laws. These state laws have proven ineffective, as illustrated by a fatal explosion of a truck transporting recalled Takata® inflators in August 2016, in Texas. In some cases, specially designed thick-walled metal containers are being used to transport recalled inflators. However, these containers are expensive to build and are not suitable for mass production on the scale required for the current recalls. Lack of a common protocol at the national and global levels for the handling, packaging, storage, and shipment of inflators containing unstable ammonium-nitrate-based propellant may result in further human injury as well as economic and environmental damage.
As a result, a need exists for a nationally implementable, low-cost method for transporting recalled inflators. Safety concerns can be addressed with a process of modifying common containers or entire vehicles to achieve a structure and method suitable for the safe, bulk transport of recalled inflators using materials that are common across the continent, nation, or state. A method of construction and validation of the proposed shipping container designs is described for both large and small scales below.